I think there is certainly a lot to question in the department's expenditure, but the colouring books may or not be one of them. Much depends on the context.

My daughter works in HR for a private firm and my daughter-in-law for MacMillian's Nurses. Both have a role in trying to ensure the wellbeing of the staff in the organisation. Personally, such colouring books do nothing for me, but I know people who say they find them helpful to de-stress.   If that 900 is say a bulk order of 300 books to be used throughout the department, it may be one of the more reasonable expenses.